A Bit on the Side

Buying a new car? Always tick the box for side airbags or curtain airbags. Here’s why

People involved in side impact collisions are three times more likely to suffer traumatic brain injury than people in head-on crashes.

Side impacts are far more likely to cause irreversible brain damage, even though side impact speed is often lower. “Half of all fatal accidents occur at an impact speed of less than 55km/h,” Australian road safety expert Michael Paine told the World Health Organisation in Sydney recently. Here’s why:

In a frontal crash there is inevitably at least 1.5 metres of metal structure that can be tuned to absorb the impact by deforming in a controlled way. Think of it as the crash mitigation equivalent of a stack of mattresses strapped in front of you. Additionally, a big, fat airbag can be fitted between you and the windscreen. These technologies act in concert to slow your head’s deceleration, and hence the loads experienced by your brain, during a crash. The crash performance requirements mandated by Australian Design Rule 69 mean there’s really no option for manufacturers other than to fit front airbags, at least for the driver.

At the side, however, there is likely to be a space of only 20cm or so comprising mostly air and a thin pane of very hard glass. Its capacity to absorb impact is negligible, which explains why side impacts at very mundane speeds like 50km/h are often fatal. When the car hits a tree or power pole, for example, it intrudes inside the cabin, too, offering almost no ‘give’.

Extreme loads on impact don’t allow much scope for quality of life afterwards (if there’s an ‘afterwards’) and the typical customer tends to be a young male. Trauma nursing specialist Julie Evans says she has lost count of the number of young brain-injured victims who she’s seen saved in the John Hunter hospital, where she works as a trauma co-ordinator, who subsequently wait there until a bed becomes available in a nursing home, on which they will spend the rest of their lives. “Unfortunately, brains often don’t get much better,” she says.

Side airbags and so-called ‘curtain’ airbags, which cover the full length of the side glass to protect even rear passengers’ heads, deploy about eight milliseconds after the collision. At around 15 or 20 milliseconds they are fully inflated, offering critical padding at just the right time to reduce the loads on victims’ heads.

The average age of Australian cars is around 10 years. There are no regulations mandating the fitting of side airbags to new cars. That means it will probably take well over 15 years before most Australian vehicle occupants benefit from this fairly elite and potentially brain-saving technology.